Beefy Boxes and Bandwidth Generously Provided by pair Networks
No such thing as a small change
 
PerlMonks  

Re: Quoted Text rule for Parse::RecDescent?

by halley (Prior)
on Aug 23, 2005 at 15:14 UTC ( #485935=note: print w/ replies, xml ) Need Help??


in reply to Quoted Text rule for Parse::RecDescent?

If you don't want anything but ' and " strings, then just fail the rule if $item[...][1] ne "'" and $item[...][1] ne '"'.

In my application, I allow qr// and ' and ", but not others like qq//, qx//, s/// or tr///. In qr//, I scan for any use of (?{...}) and fail for those. I just bring it up to show that you can choose your rules pretty flexibly.

(Expanded answer.)

As for "how to use the code blocks in a production," just realize that there's no real difference between the parsing parts and the code parts: if you get through all of the subrules in the production, then the whole production succeeds and passes whatever is in $return up to the calling rule. The code blocks in YACC are very distinct, but code blocks in P::RD are more like embedded (?{}) code in a regexp. (That was my revelation thanks to another monk a few weeks ago.)

So, do whatever you want in a code block. The items so far are in @item and %item. You can assign whatever you want to assign into $return, including undef to fail the rule.

string: <perl_quotelike> { if ($item[1][0] =~ /^(qx|s|tr|y)$/ or # no perl commands $item[1][1] eq '`' or # no backticks $item[1][2] =~ /\(\?\??\{/) # no qr'' with code { $return = undef } else { $return = eval "" . join('', @{$item[1]}) } (defined $return) }

--
[ e d @ h a l l e y . c c ]


Comment on Re: Quoted Text rule for Parse::RecDescent?
Select or Download Code
Re^2: Quoted Text rule for Parse::RecDescent?
by suaveant (Parson) on Aug 26, 2005 at 18:06 UTC
    ahhh... that helps. Though it seems a little more efficient to check
    if(!$item[1][0] && $item[1][1] eq '"' || $item[1][1] eq "'")) {

    Thanks!

                    - Ant
                    - Some of my best work - (1 2 3)

Log In?
Username:
Password:

What's my password?
Create A New User
Node Status?
node history
Node Type: note [id://485935]
help
Chatterbox?
and the web crawler heard nothing...

How do I use this? | Other CB clients
Other Users?
Others cooling their heels in the Monastery: (14)
As of 2014-08-29 13:41 GMT
Sections?
Information?
Find Nodes?
Leftovers?
    Voting Booth?

    The best computer themed movie is:











    Results (280 votes), past polls